At present, a way of exploitation by means of water injection is mostly adopted in the oilfield, and water of about 5-8 m3 is reinjected underground for exploiting every one ton of crude oil. Produced water of the oilfield is almost entirely reinjected underground after being treated. The oil yield of the oilfield is affected if the wastewater containing a considerable amount of contaminants such as suspended solid and emulsified oil is reinjected underground. Therefore, technologies and equipment for treating oilfield wastewater for reinjection are essential to the exploitation and production of the oilfield.
The traditional technologies and equipment for the treatment of wastewater with the use of two-stage sedimentation and two-stage filtration have drawbacks of a long purification process, a large system and a low purification efficiency, and thus are difficult to satisfy technology requirements for purifying the produced water enriched with emulsified oil and suspended solid. Further, the traditional technology system for the treatment of oily wastewater is disadvantageous for a low efficiency and unstable operations. Wastewater treatment technology using a ceramic ultrafiltration membrane has been studied since 1991, but is still within the industrial trial stage due to the high price of the ceramic membrane, strict pretreatment requirements and strict requirements on the cleaning of the membrane. In addition, the deoiling technology using a cyclone, although being advantageous for simple facilities and low costs, cannot obtain water qualified for the reinjection from the treatment of the produced water. For oilfields and petrochemical enterprises, therefore, there is a demanding need for new technologies and equipment for treating wastewater that have a high purification efficiency and low investment and maintenance costs, and are able to obtain water meeting the existing criterions for reinjection water or recycled water from the treatment of the produced water.